RFC Proposal: Maybe monad and execution time polymorphic methods

8 years ago by Facundo Martinez Correa — view source

unread

Hello,

I am reaching you in order to obtain feedback on this RFC proposal.

I have been playing with PHP 7 for a project in the company that I am
currently working for. One of the many drawbacks that I saw in PHP was the
there were no types. With type hinting I had confindence again in PHP. With
return type hinting a wasn't able to resist to try it. So here I am, making
a whole new platform entirely in PHP 7, using type hints in everything.
Arguments and returns alike. Given my tendency to language purity imagine
my surprise when my code inadvertently tryied to sneak a NULL into a method
expecting an object... And failing thanks to strictness in object and null
treatments in the new PHP 7. "SWEET!" I yelled.

Now imagine my dumbfoundedness when a Repository of mine tryed to return a
NULL, and because it ought to return have returned a User, it threw a
TypeError. At first I said "sweet." But then I realized the problem. There
are many times where we need uncertainty. Code is a reflection of reality,
and as such, it must reflect uncertainty. NULL is a good enough way to
express nonexistence, albeit a bad one. We have been using it in code for
years, but it is also used to say many things. Things that cause
uncertainty in the code. I receive a null, does it mean it doesn't exists?
That it will exist? Should I allow it? Is it a good value? I for sure don't
know. And in my experience, I have used it for many of those cases. And in
many situations that I'm not proud of, all of them at the same time.

So I want to "return a NULL". I want to express uncertainty, a
nonexistence. But I want to express that I will return something. And I
want to have this NULL checking at interpretation time. I want everything,
and none of the drawbacks. As we say here in Argentina, I want the bread
and the cake. What can we do to have it? After a bit of thought the Maybe
monad came to me.

My experience in Haskell reminded me of this. To have a structure than
represents uncertainty, is the best way to take away the responsibility
from NULL. To express it in no other way. But my experience in Java has
taught me that Optional of something is not a good way to tackle the
problem. I still have to check if my Optional isEmpty. I still have to
check for null. That is because Java has that type erasure after
compilation time that doesn't allow me to play nice with polymorphism. But
maybe PHP can. Maybe PHP will give me the polymorphism at execution time to
discern an empty Maybe from the one that is not. So I don't have to check
for null ever again in my life. So my code can be free of nulls. So I can
express uncertainty and nonexistance, while I return a User from my
repository.

I hope someone would like this idea. I'm also open to suggestions.
Kind regards
Facundo Martínez

8 years ago by Levi Morrison — view source

unread

My experience in Haskell reminded me of this. To have a structure than
represents uncertainty, is the best way to take away the responsibility
from NULL. To express it in no other way. But my experience in Java has
taught me that Optional of something is not a good way to tackle the
problem. I still have to check if my Optional isEmpty. I still have to
check for null. That is because Java has that type erasure after
compilation time that doesn't allow me to play nice with polymorphism. But
maybe PHP can. Maybe PHP will give me the polymorphism at execution time to
discern an empty Maybe from the one that is not. So I don't have to check
for null ever again in my life. So my code can be free of nulls. So I can
express uncertainty and nonexistance, while I return a User from my
repository.

I don't fully understand what you are asking for here. You want a
Maybe<T> to automatically become a T if it's not null or something?

8 years ago by Facundo Martinez Correa — view source

unread

Hi Levi,

Thanks for replying. I don't think that automagically taking the T out of
the Maybe<T> would be a good idea, mainly because sometimes you don't need
the T, you just want to know the result of it. What I would want in that
PHP automagically executes the method myMethod(Maybe<T> $object) if
something was returned or the method myMethod(EmptyMaybe $object) if the
returned was an EmptyMaybe.

The use of Maybe is, in fact, a motivation for real operators oveloading.
The kind that will be decided at execution time, with the type at hand.
This motivation came when what I explained happened. And that's the reason
why I'm also sugesting a Maybe.

Regards,

My experience in Haskell reminded me of this. To have a structure than
represents uncertainty, is the best way to take away the responsibility
from NULL. To express it in no other way. But my experience in Java has
taught me that Optional of something is not a good way to tackle the
problem. I still have to check if my Optional isEmpty. I still have to
check for null. That is because Java has that type erasure after
compilation time that doesn't allow me to play nice with polymorphism.
But
maybe PHP can. Maybe PHP will give me the polymorphism at execution time
to
discern an empty Maybe from the one that is not. So I don't have to check
for null ever again in my life. So my code can be free of nulls. So I can
express uncertainty and nonexistance, while I return a User from my
repository.

I don't fully understand what you are asking for here. You want a
Maybe<T> to automatically become a T if it's not null or something?

8 years ago by Stephen Coakley — view source

unread

So I want to "return a NULL". I want to express uncertainty, a
nonexistence. But I want to express that I will return something. And I
want to have this NULL checking at interpretation time. I want everything,
and none of the drawbacks. As we say here in Argentina, I want the bread
and the cake. What can we do to have it? After a bit of thought the Maybe
monad came to me.

My experience in Haskell reminded me of this. To have a structure than
represents uncertainty, is the best way to take away the responsibility
from NULL. To express it in no other way. But my experience in Java has
taught me that Optional of something is not a good way to tackle the
problem. I still have to check if my Optional isEmpty. I still have to
check for null. That is because Java has that type erasure after
compilation time that doesn't allow me to play nice with polymorphism. But
maybe PHP can. Maybe PHP will give me the polymorphism at execution time to
discern an empty Maybe from the one that is not. So I don't have to check
for null ever again in my life. So my code can be free of nulls. So I can
express uncertainty and nonexistance, while I return a User from my
repository.

I hope someone would like this idea. I'm also open to suggestions.
Kind regards
Facundo Martínez

First of all, let me confess that I absolutely love monad (or composite)
types, and I greatly prefer a Maybe over something that may or may not
be null. There's a slight problem however, and something that will not
be easy to get around: a lack of generics.

This is an issue with wrapper types in general in PHP, where you want to
wrap an object in some other type. You lose type safety on the inner
object, and so I tend to look for a more type-safe solution in PHP.
There is already a generics RFC out there
(https://wiki.php.net/rfc/generics) but implementing it won't be trivial.

Implementing (or defining) a good Maybe type also depends on better
composite/enum types (https://wiki.php.net/rfc/enum is drafted, but
doesn't support what we need). The classical definition would be
(hypothetical PHP syntax):

enum Maybe<T>
{
Some {
public function __construct(T $value);
public function isSome(): bool {
return true;
}
public function into(): T {
return $this->value;
}
},
None {
public function isSome(): bool {
return false;
}
public function into(): T {
throw new Error();
}
}
}

Such a definition depends on two different things we don't have right
now in PHP. Maybe there's a simpler way, but hopefully you have a better
alternative?

--
Stephen

8 years ago by Levi Morrison — view source

unread

So I want to "return a NULL". I want to express uncertainty, a
nonexistence. But I want to express that I will return something. And I
want to have this NULL checking at interpretation time. I want everything,
and none of the drawbacks. As we say here in Argentina, I want the bread
and the cake. What can we do to have it? After a bit of thought the Maybe
monad came to me.

My experience in Haskell reminded me of this. To have a structure than
represents uncertainty, is the best way to take away the responsibility
from NULL. To express it in no other way. But my experience in Java has
taught me that Optional of something is not a good way to tackle the
problem. I still have to check if my Optional isEmpty. I still have to
check for null. That is because Java has that type erasure after
compilation time that doesn't allow me to play nice with polymorphism. But
maybe PHP can. Maybe PHP will give me the polymorphism at execution time
to
discern an empty Maybe from the one that is not. So I don't have to check
for null ever again in my life. So my code can be free of nulls. So I can
express uncertainty and nonexistance, while I return a User from my
repository.

I hope someone would like this idea. I'm also open to suggestions.
Kind regards
Facundo Martínez

First of all, let me confess that I absolutely love monad (or composite)
types, and I greatly prefer a Maybe over something that may or may not be
null. There's a slight problem however, and something that will not be easy
to get around: a lack of generics.

This is an issue with wrapper types in general in PHP, where you want to
wrap an object in some other type. You lose type safety on the inner object,
and so I tend to look for a more type-safe solution in PHP. There is already
a generics RFC out there (https://wiki.php.net/rfc/generics) but
implementing it won't be trivial.

Implementing (or defining) a good Maybe type also depends on better
composite/enum types (https://wiki.php.net/rfc/enum is drafted, but doesn't
support what we need). The classical definition would be (hypothetical PHP
syntax):

enum Maybe<T>
{
Some {
public function __construct(T $value);
public function isSome(): bool {
return true;
}
public function into(): T {
return $this->value;
}
},
None {
public function isSome(): bool {
return false;
}
public function into(): T {
throw new Error();
}
}
}

Such a definition depends on two different things we don't have right now in
PHP. Maybe there's a simpler way, but hopefully you have a better
alternative?

This requires you to query state with isSome(). This is hardly any
different from a null case, just more code. We can already accurately
distinguish between null and another value.

If we want an option for safer PHP code I think we need a safer
construct that requires exhaustive matching (such as Rust's match).
I'm not sure how to pull that off.

8 years ago by Stephen Coakley — view source

unread

This requires you to query state with isSome(). This is hardly any
different from a null case, just more code. We can already accurately
distinguish between null and another value.

If we want an option for safer PHP code I think we need a safer
construct that requires exhaustive matching (such as Rust's match).
I'm not sure how to pull that off.

Certainly. Ideally some sort of match, which is listed as future scope
in the enum RFC. The above definition of a Maybe is just some sort of
basis for a type. You probably wouldn't use isSome() much and would
use pattern matching on the enum instead.

As much as I do love Rust's type system though, PHP isn't Rust. :)

--
Stephen

8 years ago by Larry Garfield — view source

unread

This requires you to query state with isSome(). This is hardly any
different from a null case, just more code. We can already accurately
distinguish between null and another value.

If we want an option for safer PHP code I think we need a safer
construct that requires exhaustive matching (such as Rust's match).
I'm not sure how to pull that off.

Certainly. Ideally some sort of match, which is listed as future
scope in the enum RFC. The above definition of a Maybe is just some
sort of basis for a type. You probably wouldn't use isSome() much
and would use pattern matching on the enum instead.

As much as I do love Rust's type system though, PHP isn't Rust. :)

Correct. So we should just sneak up behind Rust, pick it's pocket, and
steal the bits that we can make work for us. That's what PHP's always
done to every other language we've encountered. :-)

--
--Larry Garfield

8 years ago by come@opensides.be — view source

unread

Le lundi 21 mars 2016, 17:04:30 Facundo Martinez Correa a écrit :

But then I realized the problem. There
are many times where we need uncertainty. Code is a reflection of reality,
and as such, it must reflect uncertainty. NULL is a good enough way to
express nonexistence, albeit a bad one. We have been using it in code for
years, but it is also used to say many things. Things that cause
uncertainty in the code. I receive a null, does it mean it doesn't exists?
That it will exist? Should I allow it? Is it a good value? I for sure don't
know. And in my experience, I have used it for many of those cases. And in
many situations that I'm not proud of, all of them at the same time.

If your function is supposed to return a User and can’t, maybe it should throw an Exception.
Just wanted to point out it can be a good alternative to returning NULL for error handling.

Côme

8 years ago by Larry Garfield — view source

unread

Le lundi 21 mars 2016, 17:04:30 Facundo Martinez Correa a écrit :

But then I realized the problem. There
are many times where we need uncertainty. Code is a reflection of reality,
and as such, it must reflect uncertainty. NULL is a good enough way to
express nonexistence, albeit a bad one. We have been using it in code for
years, but it is also used to say many things. Things that cause
uncertainty in the code. I receive a null, does it mean it doesn't exists?
That it will exist? Should I allow it? Is it a good value? I for sure don't
know. And in my experience, I have used it for many of those cases. And in
many situations that I'm not proud of, all of them at the same time.
If your function is supposed to return a User and can’t, maybe it should throw an Exception.
Just wanted to point out it can be a good alternative to returning NULL for error handling.

Côme

In the PHP 7 and typing presentations I've been giving[1], I've
advocated either:

Throw an exception if the rest of the code is going to break anyway.
Define an empty object with matching interface if you want an
equivalent of 0/empty string.

While a monad sounds cool, it doesn't seem like the necessary language
infrastructure is there for it at the moment.

[1] My most recent talk that has a section on returns:
https://youtu.be/rWDY4-LJils?t=2m38s (that's where the return type
segment starts)
Slides:

https://www.palantir.net/presentations/midcamp2016-php7/

--
--Larry Garfield

8 years ago by Andreas Heigl — view source

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Am 22.03.2016 um 15:56 schrieb Larry Garfield larry@garfieldtech.com:

Le lundi 21 mars 2016, 17:04:30 Facundo Martinez Correa a écrit :

But then I realized the problem. There
are many times where we need uncertainty. Code is a reflection of reality,
and as such, it must reflect uncertainty. NULL is a good enough way to
express nonexistence, albeit a bad one. We have been using it in code for
years, but it is also used to say many things. Things that cause
uncertainty in the code. I receive a null, does it mean it doesn't exists?
That it will exist? Should I allow it? Is it a good value? I for sure don't
know. And in my experience, I have used it for many of those cases. And in
many situations that I'm not proud of, all of them at the same time.
If your function is supposed to return a User and can’t, maybe it should throw an Exception.
Just wanted to point out it can be a good alternative to returning NULL for error handling.

Côme

In the PHP 7 and typing presentations I've been giving[1], I've advocated either:

Throw an exception if the rest of the code is going to break anyway.

Define an empty object with matching interface if you want an equivalent of 0/empty string.

When code expects a user-object but can't get one it'll break. Throwing an exception makes it easy to react to that. But when the code has to check whether that's a mocked user object or a real user object it's about as good as returning null or eliminating the return type altogether as you have to build the code around that returned value you can't really use.

So in my opinion either return a proper object/type or throw an exception.

My 2 cent

Cheers

Andreas

While a monad sounds cool, it doesn't seem like the necessary language infrastructure is there for it at the moment.

[1] My most recent talk that has a section on returns:
https://youtu.be/rWDY4-LJils?t=2m38s (that's where the return type segment starts)
Slides:

https://www.palantir.net/presentations/midcamp2016-php7/

--
--Larry Garfield

8 years ago by Larry Garfield — view source

unread

Am 22.03.2016 um 15:56 schrieb Larry Garfield larry@garfieldtech.com:

Le lundi 21 mars 2016, 17:04:30 Facundo Martinez Correa a écrit :

But then I realized the problem. There
are many times where we need uncertainty. Code is a reflection of reality,
and as such, it must reflect uncertainty. NULL is a good enough way to
express nonexistence, albeit a bad one. We have been using it in code for
years, but it is also used to say many things. Things that cause
uncertainty in the code. I receive a null, does it mean it doesn't exists?
That it will exist? Should I allow it? Is it a good value? I for sure don't
know. And in my experience, I have used it for many of those cases. And in
many situations that I'm not proud of, all of them at the same time.
If your function is supposed to return a User and can’t, maybe it should throw an Exception.
Just wanted to point out it can be a good alternative to returning NULL for error handling.

Côme
In the PHP 7 and typing presentations I've been giving[1], I've advocated either:

Throw an exception if the rest of the code is going to break anyway.

Define an empty object with matching interface if you want an equivalent of 0/empty string.
When code expects a user-object but can't get one it'll break. Throwing an exception makes it easy to react to that. But when the code has to check whether that's a mocked user object or a real user object it's about as good as returning null or eliminating the return type altogether as you have to build the code around that returned value you can't really use.

So in my opinion either return a proper object/type or throw an exception.

An "empty" object as I describe it isn't really a proper empty object
unless it does satisfy the type and interface, such that you don't need
special handling for it. The example I use in the slides is an Address
object, with AddressInterface, whose "empty" implementation just has
empty strings for all the various parts of it. That will work in some
use cases but not others. It's up to the developer to determine if a
reasonable empty object would work in their situation or not. If it
doesn't, I agree, an exception is the answer.

In any event, it sounds like a native monad won't work well in PHP so
we're now drifting off topic. :-)

--
--Larry Garfield

8 years ago by Rowan Collins — view source

unread

Andreas Heigl wrote on 22/03/2016 16:25:

In the PHP 7 and typing presentations I've been giving[1], I've advocated either:

Throw an exception if the rest of the code is going to break anyway.

Define an empty object with matching interface if you want an equivalent of 0/empty string.
When code expects a user-object but can't get one it'll break. Throwing an exception makes it easy to react to that. But when the code has to check whether that's a mocked user object or a real user object it's about as good as returning null or eliminating the return type altogether as you have to build the code around that returned value you can't really use.

It depends on the context; sometimes, you are right, you would end up
checking for validity early anyway, and an exception would be easier.
However, the Null Object Pattern can simplify logic significantly where
there is an obvious "null behaviour" that it can implement.

Wikipedia gives the example of a recursive tree operation having to
check for missing child nodes
(https://en.wikipedia.org/wiki/Null_Object_pattern#Example);
initialising the child nodes with Null Objects eliminates the check.

The key point is that in some cases, the calling code won't break,
because the Null Object can still adhere to the interface, just by
returning appropriate empty values. In the tree node case, a
NullTreeNode would always return further NullTreeNodes as children, a
sub-tree size of 0, and either no-op or error if you attempted modification.

Regards,

Rowan Collins
[IMSoP]

8 years ago by Kubo2 — view source

unread

Hi Facundo Martínez,

I think the best solution to yourself described problem above would be
the Null Object Design Pattern
(https://en.wikipedia.org/wiki/Null_Object_pattern). In my opinion,
NULL belongs to PHP and this language never aimed to become Java or
similar.

Jakub

On 22 March 2016 at 01:34, Facundo Martinez Correa
fnmartinez88@gmail.com wrote:

Hello,

I am reaching you in order to obtain feedback on this RFC proposal.

I have been playing with PHP 7 for a project in the company that I am
currently working for. One of the many drawbacks that I saw in PHP was the
there were no types. With type hinting I had confindence again in PHP. With
return type hinting a wasn't able to resist to try it. So here I am, making
a whole new platform entirely in PHP 7, using type hints in everything.
Arguments and returns alike. Given my tendency to language purity imagine
my surprise when my code inadvertently tryied to sneak a NULL into a method
expecting an object... And failing thanks to strictness in object and null
treatments in the new PHP 7. "SWEET!" I yelled.

Now imagine my dumbfoundedness when a Repository of mine tryed to return a
NULL, and because it ought to return have returned a User, it threw a
TypeError. At first I said "sweet." But then I realized the problem. There
are many times where we need uncertainty. Code is a reflection of reality,
and as such, it must reflect uncertainty. NULL is a good enough way to
express nonexistence, albeit a bad one. We have been using it in code for
years, but it is also used to say many things. Things that cause
uncertainty in the code. I receive a null, does it mean it doesn't exists?
That it will exist? Should I allow it? Is it a good value? I for sure don't
know. And in my experience, I have used it for many of those cases. And in
many situations that I'm not proud of, all of them at the same time.

So I want to "return a NULL". I want to express uncertainty, a
nonexistence. But I want to express that I will return something. And I
want to have this NULL checking at interpretation time. I want everything,
and none of the drawbacks. As we say here in Argentina, I want the bread
and the cake. What can we do to have it? After a bit of thought the Maybe
monad came to me.

My experience in Haskell reminded me of this. To have a structure than
represents uncertainty, is the best way to take away the responsibility
from NULL. To express it in no other way. But my experience in Java has
taught me that Optional of something is not a good way to tackle the
problem. I still have to check if my Optional isEmpty. I still have to
check for null. That is because Java has that type erasure after
compilation time that doesn't allow me to play nice with polymorphism. But
maybe PHP can. Maybe PHP will give me the polymorphism at execution time to
discern an empty Maybe from the one that is not. So I don't have to check
for null ever again in my life. So my code can be free of nulls. So I can
express uncertainty and nonexistance, while I return a User from my
repository.

I hope someone would like this idea. I'm also open to suggestions.
Kind regards
Facundo Martínez

--
Cheers,
Kubis

8 years ago by Facundo Martinez Correa — view source

unread

Hi Jakub,

Regarding the Null Object, I believe it to be a second hand solution.
Having a Null Object that returns 0, null, "" or false for every method
call, or a nil that acts as in Objective C that doesn't tell you when is
being poked the wrong way is the first step into madness. It will never
tell you about runtime errors, and you will find those errors once some
data that is being outputed from the systems gets into your
DB/Logs/Screen/whatever and just by chance you see that and say "Hey! that
wasn't supposed to be there!". Then all hell breaks loose, and you start
chasing code that never happens because your data will never be wrong and
will always gracefully degrade. I believe that pattern is a bad pattern and
humanity should feel bad about it. In fact, I believe it will be a feature
that will drive people away from PHP and not towards it.
Besides, the whole point of this idea I brought was to avoid checks that
the interpreter could catch. If I return a Null Object, I'm forced to
always ask for it.

Now, regarding the "NULL belongs to PHP and this language never aimed to
become Java" part. That is interesting because
a) I never wanted to be Java, and in fact, I want it to be as more
different to it as possible because I know what is bad and good and Java.
b) As far as I remember, from the beginning of PHP, NULL was as in C a
rename for 0. You could use 0, FALSE and NULL indistinctly. I'm not saying
to eliminate null. Null does serve some other purposes, specially when you
are managing memory, or bits, or whatever. I'm talking about making it
represent less things and make the language more expressive.

I hope transmitted my idea right. Thanks for the reply,
Facundo

Hi Facundo Martínez,

I think the best solution to yourself described problem above would be
the Null Object Design Pattern
(https://en.wikipedia.org/wiki/Null_Object_pattern). In my opinion,
NULL belongs to PHP and this language never aimed to become Java or
similar.

Jakub

On 22 March 2016 at 01:34, Facundo Martinez Correa
fnmartinez88@gmail.com wrote:

Hello,

I am reaching you in order to obtain feedback on this RFC proposal.

I have been playing with PHP 7 for a project in the company that I am
currently working for. One of the many drawbacks that I saw in PHP was
the
there were no types. With type hinting I had confindence again in PHP.
With
return type hinting a wasn't able to resist to try it. So here I am,
making
a whole new platform entirely in PHP 7, using type hints in everything.
Arguments and returns alike. Given my tendency to language purity imagine
my surprise when my code inadvertently tryied to sneak a NULL into a
method
expecting an object... And failing thanks to strictness in object and
null
treatments in the new PHP 7. "SWEET!" I yelled.

Now imagine my dumbfoundedness when a Repository of mine tryed to return
a
NULL, and because it ought to return have returned a User, it threw a
TypeError. At first I said "sweet." But then I realized the problem.
There
are many times where we need uncertainty. Code is a reflection of
reality,
and as such, it must reflect uncertainty. NULL is a good enough way to
express nonexistence, albeit a bad one. We have been using it in code for
years, but it is also used to say many things. Things that cause
uncertainty in the code. I receive a null, does it mean it doesn't
exists?
That it will exist? Should I allow it? Is it a good value? I for sure
don't
know. And in my experience, I have used it for many of those cases. And
in
many situations that I'm not proud of, all of them at the same time.

So I want to "return a NULL". I want to express uncertainty, a
nonexistence. But I want to express that I will return something. And I
want to have this NULL checking at interpretation time. I want
everything,
and none of the drawbacks. As we say here in Argentina, I want the bread
and the cake. What can we do to have it? After a bit of thought the Maybe
monad came to me.

My experience in Haskell reminded me of this. To have a structure than
represents uncertainty, is the best way to take away the responsibility
from NULL. To express it in no other way. But my experience in Java has
taught me that Optional of something is not a good way to tackle the
problem. I still have to check if my Optional isEmpty. I still have to
check for null. That is because Java has that type erasure after
compilation time that doesn't allow me to play nice with polymorphism.
But
maybe PHP can. Maybe PHP will give me the polymorphism at execution time
to
discern an empty Maybe from the one that is not. So I don't have to check
for null ever again in my life. So my code can be free of nulls. So I can
express uncertainty and nonexistance, while I return a User from my
repository.

I hope someone would like this idea. I'm also open to suggestions.
Kind regards
Facundo Martínez

--
Cheers,
Kubis

8 years ago by Stanislav Malyshev — view source

unread

Hi!

maybe PHP can. Maybe PHP will give me the polymorphism at execution time to
discern an empty Maybe from the one that is not. So I don't have to check

In order for that to work, we should have a facility to:
a) define union types
b) ensure somehow that code dealing with the union type covers all variants
c) if we really want to be able to handle such types smoothly, we need
something like monads to be able to convert f(SomeClass $x) to f(Maybe $x).

This does not sound trivial at all. (c) is not strictly required for the
rest to work, but will also require some kind of generics, since Maybe
should have information about contained type (maybe what? maybe file,
maybe database connection, maybe pastrami sandwich?). If you give up on
(c), you still need some facility like case-of for (b).

And, of course, you will still need to write code to cover the "nothing"
case of the Maybe. So it might be easier getting a code analyzer that
would just identify missing null checks?

--
Stas Malyshev
smalyshev@gmail.com

8 years ago by Facundo Martinez Correa — view source

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Hi Stanislav,

Yes, as you are saying, it is no easy task. I believe it would make a nice
feature, though. I don't know it is really necessary to use union types, I
believe that with a class hierarchy would suffice. But maybe there is
something that I'm not looking at right, and the unions are needed. It
would certainly need some kind of generics or templates, though I don't
know how powerfull they ought to be. In fact, having generics was something
that also came into my mind when dealing with this project, since I would
use the Builder Patter for my Entities, had a couple of Entities that
extended one from the other and I couldn't play it nice with the Type
Hinting.

Maybe is as Jakub told me, and PHP is not aiming to be Java nor anything
similar in anyway. But I believe that if it is moving into type checking,
it means that the community is seeing it as something needed. So it would
be interesting maybe to have something similar to TypeScript, something
like Gradual Typing. But to have that, everything from both worlds must
work.

Thanks for the reply.
Kind regards,
Facundo

On Mon, Mar 28, 2016 at 9:13 PM, Stanislav Malyshev smalyshev@gmail.com
wrote:

Hi!

maybe PHP can. Maybe PHP will give me the polymorphism at execution time
to
discern an empty Maybe from the one that is not. So I don't have to check

In order for that to work, we should have a facility to:
a) define union types
b) ensure somehow that code dealing with the union type covers all variants
c) if we really want to be able to handle such types smoothly, we need
something like monads to be able to convert f(SomeClass $x) to f(Maybe $x).

This does not sound trivial at all. (c) is not strictly required for the
rest to work, but will also require some kind of generics, since Maybe
should have information about contained type (maybe what? maybe file,
maybe database connection, maybe pastrami sandwich?). If you give up on
(c), you still need some facility like case-of for (b).

And, of course, you will still need to write code to cover the "nothing"
case of the Maybe. So it might be easier getting a code analyzer that
would just identify missing null checks?

--
Stas Malyshev
smalyshev@gmail.com